1. Field of the Invention
The present invention relates to an electrostatic actuator to be used as a driving mechanism of an ink-jet head and the like, a droplet discharge head, a method for driving a droplet discharge head, and a method for manufacturing an electrostatic actuator.
2. Description of the Related Art
Examples of droplet discharge head previously include a thermal type droplet discharge head by using a heat generating element or the like as a driving device and an actuator drive type droplet discharge head. Examples of actuator drive types include a so-called electrostatic drive type, in which an electrostatic force is used as a driving device, and a so-called piezoelectric drive type, in which a piezoelectric element (piezo element) is used.
In the actuator drive type droplet discharge head, a diaphragm constituting a part of a discharge chamber is elastically displaced on the basis of an electrostatic force or a piezoelectric effect of a piezoelectric element, a pressure is generated in a pressure chamber and, thereby, droplets are discharged from a nozzle. For this type of droplet discharge head, in recent years, a multi-nozzle has been used in order to address the high-speed printing. Furthermore, a miniaturized actuator has been required to meet the demands on higher resolution. However, as the actuator is miniaturized and is made denser, the displacement of the diaphragm becomes inadequate. Consequently, there is a problem in that an adequate pressure is not generated in the pressure chamber and a required amount of discharge of droplets cannot be attained.
For piezoelectric drive type droplet discharge apparatuses, a multilayered inorganic electret layer is disposed on a diaphragm to attain a large mechanical driving force and, thereby, the displacement of the diaphragm is increased (for example, Patent Document 1), or a diaphragm is allowed to have a configuration in which an inorganic electret layer and a thin film metal heating pattern are laminated, the electret layer is deformed by application of a voltage and, in addition, the electret layer is expanded by the thin film metal heating pattern, so that the diaphragm is displaced by a large degree (for example, Patent Document 2).
With respect to the electret layer, in addition to the above described technology for applying the electret layer to the droplet discharge head, there is a configuration in which at least one pair of opposed electrodes are disposed on an ink flow path side wall, and one of the pair of electrodes includes the electret layer (for example, Patent Document 3).    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-255605    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2004-255614    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2000-280490
In the technology of Patent Document 1, the multilayered inorganic electret layer is disposed on a diaphragm, and the thickness of the diaphragm must be increased to support it. In the technology of Patent Document 2, the diaphragm itself is composed of a multilayer and, likewise, the thickness of the diaphragm is increased. The above-described configurations have problems in that the mechanical resistance is increased, it is difficult to actually attain a diaphragm displacement adequate for stably discharging droplets, and the driving voltage must be increased to attain an adequate diaphragm displacement. Furthermore, there is a problem in that the manufacturing method is complicated and it is difficult to manufacture.
Patent Document 3 discloses the technology in which the electret layer is used for the droplet discharge head in order to improve the ink bubble discharging property. However, there is no specific discussion on the reduction of driving voltage.